Transition Metal and group 2 Model Answers Flashcards
(36 cards)
Method of UV-Visible spectroscopy
Standard solution of known conc is made up
Serial dilutions are made to get at least 5 different known concentrations that range around the unknown concentration
The absorbance of each solution is measured by passing the complementary colour of light through the solution
The absorbance of the unknown solution is measured
A graph is plotted: absorbance vs known conc
Graph is used to determine conc of unknown solution by reading absorbance
Properties of transition metals
Form complex ions
Form coloured ions in solution
Have variable oxidation states
Show catalytic activity
Complex ion
Central metal ion or atom surrounded by ligands
Ligand
Molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons
Coordination number
Number of coordinate bonds to central metal atom or ion
Naming ions: chloride, cyanide, hydroxide, ammonia, water
Chloro cyano hydroxo ammine aqua
Which order do ligands come in
Negative then neutral
If same charge, alphabetical
Naming ions: copper, manganese, chromium, silver, iron, vanadium, cobalt
Cuprate, manganate, chromate, argentate, ferrate, vanadate, cobaltate
When does copper become cuprate?
If ion has overall negative charge
Why do transition metals form coloured compounds? (5)
d-subshells split
Electrons absorb visible light and move to higher d-orbital
E=hf
Wavelengths not absorbed are transmitted or reflected
How does haemoglobin enable oxygen to be transported in the blood?
Oxygen forms co-ordinate bond to Fe(II) in haemoglobin
Linear complex example
[Ag(NH3)2]
Tetrahedral complex example
[CoCl4]2-
Square planar complex example
[PtCl2(NH3)2]
Method for UV-visible spectroscopy
Make up 5 solutions of known concentration
Measure absorbance of complementary colour
Distilled water to set absorbance at 0
Plot calibration curve
Measure absorbance of unknown concentration
Use graph to determine unknown concentration
Vanadium oxidation states, ion formulae and colours
V(2+) purple +2
V(3+) green +3
VO(2+) blue +4
VO2 (+) yellow +5
If exposed to air what happens to V(2+)
Oxidises to V(3+)
Precise colours of vanadium solutions depends on
Acids used
Catalyst definition
Substance that increases rate of chemical reaction
Without being used up
How does catalyst work?
Provide alternative reaction pathway with lower activation energy
How do variable oxidation states allow TM to act as catalysts?
Transition metal provides alternative route for reaction to take place by first changing oxidation state then changing back to original oxidation state
How can you increase surface area of catalyst?
Grind into powder
Convert solid into mesh
Examples of catalyst poisoning
Sulfur poisoning in Haber process
Lead poisoning in catalytic converters
Why does catalyst need to be Goldilocks?
If adsorption too strong, molecules can’t move around the active sites and product can’t be released from the active sites
If adsorption too weak, not many molecules will be adsorbed and surface concentration will be too low
